Authorities have identified a Belgian named Oussama Atar as the possible organiser of deadly Islamic State attacks on Paris and Brussels over the past year.
A judicial official and a security official said Atar's name appears in the investigation.
The judicial official said there is evidence that Atar is the real identity of Abu Ahmed, a pseudonym of the suspected attack coordinator. His whereabouts are unknown.
Atar's name has been circulating in Belgium for months as possibly linked to the attacks.
Investigators believe the same IS cell was behind the Paris attacks in November 2015 and the Brussels attacks in March, which together killed 162 people.